Bud Set Research Articles

Trembling aspen seedling establishment, growth and response to fertilization on contrasting soils used in oil sands reclamation

Pinno, B. D., Landhäusser, S. M., MacKenzie, M. D., Quideau, S. A. and Chow, P. S. 2012. Trembling aspen seedling establishment, growth and response to fertilization on contrasting soils used in oil sands reclamation. Can. J. Soil Sci. 92: 143–151. Trembling aspen (Populus tremuloides) is an important tree species for land reclamation. This study determined trembling aspen germination, establishment, initial growth and response to fertilizer on contrasting oil sands reclamation soils. In a greenhouse, eight soils varying in total nitrogen and available phosphorus were treated with no fertilizer (control), phosphorus and potassium (PK), nitrogen (N) and all three (NPK). Soil had the greatest impact on aspen growth when no fertilizer was applied with the best growth occurring on organic-mineral material soils where growth was positively correlated with extractable and foliar potassium but not to nitrogen or phosphorus. With PK and N fertilizer, growth increases were positively correlated with foliar phosphorus concentrations of the corresponding controls. NPK fertilizer caused greater growth, bud set and root:leaf mass ratio compared with PK or N fertilizer. Soil type had little impact on germination and establishment, indicating natural aspen seedlings can potentially regenerate on all of these soils. In oil sands mining reclamation where these soils are used as surface materials, organic-mineral mixes had the greatest potential without fertilizer. With fertilizer, NPK provided maximum growth and developmental benefits.

Immediate and residual effects of prohexadione-calcium, with or without ethephon, applied in a low-pH solution on vegetative and reproductive growth in sweet cherry trees (Prunus avium L.)

SummaryA single application of either prohexadione-calcium (Ca) at 250 mg l–1, or of prohexadione-Ca at 250 mg l–1 plus ethephon at 180 mg l–1, dissolved in water acidified with 1.0 g l–1 citric acid was applied to young ‘Burlat’ sweet cherry trees (Prunus avium L.). In the year of application, both chemicals provided effective growth control over the entire season, with prohexadione-Ca plus ethephon being more restrictive to growth than prohexadione-Ca alone. This pattern of growth suppression was observed in the dynamics of shoot elongation, mean shoot length, internode length, and total shoot extension. Both chemical treatments increased flower bud set on previous-season shoots. Residual effects (i.e., in the year following treatment, with no additional chemical application) were produced by prohexadione-Ca plus ethephon, which reduced the mean shoot length to 56.6% of untreated control trees, and by both treatments significantly limiting the length of all internodes relative to the controls. No residual effects were observed on the numbers of flower buds in year-2.

Does past emergence of epicormic shoots control current composition of epicormic types?

While past studies on epicormics in oak (Quercus sp.) have focused on the effect of thinning on epicormic shoots emergence, the consequences of this emergence on the epicormic ontogeny and future wood quality have rarely been asked. This paper aims to quantifying the relationship between past emergence and current composition of epicormics. Three thinning experiments with Quercus petraea (Matt.) Liebl. or Quercus robur L. were investigated. Epicormic shoots were regularly tallied and epicormic composition recorded recently. Some logs were scanned using X-ray computed tomography (CT). Past tallies on both species were mainly and positively related to the current frequency of bud clusters and burls. This was due to the production of buds by epicormic shoots for only certain trees, as evidenced by CT, and mainly to correlated numbers of current epicormic shoots, bud clusters and burls, all originating from a past common set of buds and bud clusters. The important tree effect on both species suggests that oak silviculture can be optimized by the early selection of crop trees with few epicormics and/or eventually a first and heavy thinning that helps in spotting remaining individuals being prone to the development of multiple epicormics.

Short Day–Mediated Cessation of Growth Requires the Downregulation of AINTEGUMENTALIKE1 Transcription Factor in Hybrid Aspen

Day length is a key environmental cue regulating the timing of major developmental transitions in plants. For example, in perennial plants such as the long-lived trees of the boreal forest, exposure to short days (SD) leads to the termination of meristem activity and bud set (referred to as growth cessation). The mechanism underlying SD–mediated induction of growth cessation is poorly understood. Here we show that the AIL1-AIL4 (AINTEGUMENTALIKE) transcription factors of the AP2 family are the downstream targets of the SD signal in the regulation of growth cessation response in hybrid aspen trees. AIL1 is expressed in the shoot apical meristem and leaf primordia, and exposure to SD signal downregulates AIL1 expression. Downregulation of AIL gene expression by SDs is altered in transgenic hybrid aspen plants that are defective in SD perception and/or response, e.g. PHYA or FT overexpressors. Importantly, SD–mediated regulation of growth cessation response is also affected by overexpression or downregulation of AIL gene expression. AIL1 protein can interact with the promoter of the key cell cycle genes, e.g. CYCD3.2, and downregulation of the expression of D-type cyclins after SD treatment is prevented by AIL1 overexpression. These data reveal that execution of SD–mediated growth cessation response requires the downregulation of AIL gene expression. Thus, while early acting components like PHYA and the CO/FT regulon are conserved in day-length regulation of flowering time and growth cessation between annual and perennial plants, signaling pathways downstream of SD perception diverge, with AIL transcription factors being novel targets of the CO/FT regulon connecting the perception of SD signal to the regulation of meristem activity.

Genetic and environmental influences on leaf phenology and cold hardiness of native and introduced riparian trees

To explore the roles of plasticity and genetic variation in the response to spatial and temporal climate variation, we established a common garden consisting of paired collections of native and introduced riparian trees sampled along a latitudinal gradient. The garden in Fort Collins, Colorado (latitude 40.6°N), included 681 native plains cottonwood (Populus deltoides subsp. monilifera) and introduced saltcedar (Tamarix ramosissima, T. chinensis and hybrids) collected from 15 sites at 29.2-47.6°N in the central United States. In the common garden both species showed latitudinal variation in fall, but not spring, leaf phenology, suggesting that the latitudinal gradient in fall phenology observed in the field results at least in part from inherited variation in the critical photoperiod, while the latitudinal gradient in spring phenology observed in the field is largely a plastic response to the temperature gradient. Populations from higher latitudes exhibited earlier bud set and leaf senescence. Cold hardiness varied latitudinally in both fall and spring for both species. For cottonwood, cold hardiness began earlier and ended later in northern than in southern populations. For saltcedar northern populations were hardier throughout the cold season than southern populations. Although cottonwood was hardier than saltcedar in midwinter, the reverse was true in late fall and early spring. The latitudinal variation in fall phenology and cold hardiness of saltcedar appears to have developed as a result of multiple introductions of genetically distinct populations, hybridization and natural selection in the 150 years since introduction.

Molecular dissection of an adaptive epigenetic memory mechanism in norway spruce

Molecular dissection of an adaptive epigenetic memory mechanism in norway spruce

Analysis of expression patterns of candidate genes for bud set and cold tolerance in scots pine (Pinus sylvestris l.)

Conifers, like other perennial plants adapt their growth rhythm to seasonal changes in the environment. Growth cessation and bud set are among the main adaptations used by the plants to prepare for winter. These adaptive traits are mainly controlled by photoperiod, temperature and light quality and show a clinal variation in different species including Scots pine. In conifers, efforts have been made to understand the genetic basis of these traits. In Norway spruce for instance, a Flowering Locus T homolog (PaFT4) has been shown to be implicated in the control of growth rhythm. We previously evaluated genetic variation for timing of bud set and cold tolerance in a large association population of Scots pine (Pinus sylvestris L.) from Punkaharju, Southern Finland, along with five other populations used as control for clinal variation. To correlate this genetic variation with the expression pattern of some candidate genes already described in other species including conifers as involved in the control of bud set (e.g. FT4, PRR1, Gi, Myb) and cold tolerance (e.g. Aba responsive, DHN3, ERD, LEA), the Punkaharju population was used together with two others from Kolari (Northern Finland) and Poland. For photoperiod treatments, seedlings of eight families from each population were grown in a greenhouse under natural photoperiod conditions and in growth chambers under constant light for three months before transfer to three different photoperiod conditions (20 h/4 h, 17 h/7 h and 8 h/16 h light/dark). For cold treatments, the same families were grown in growth chambers under constant light for two and a half months and divided into two parts. The first part was directly submitted to the cold treatments (+4°C for one week followed by -5°C for 48 hours) while for the second part, seedlings were allowed to set buds under short day conditions (8 h light/16 h dark) before treatments. The results of this expression study will be described in relation to the phenotypic variance already observed.

A roadmap of apical bud formation in white spruce identifies potential regulators of time to bud set

Background Bud development is an adaptation that temperate forest trees have acquired to survive inclement winter conditions and resume growth the following spring. Bud development is a complex physiological and developmental process comprising bud formation, cold and desiccation tolerance development, and dormancy acquisition [1]. Because bud formation is accompanied by growth cessation, the timing of bud formation represents a trade-off between acquisition of winter hardiness and duration of active growth [2]. This is particularly true for determinate species such as white spruce (Picea glauca [Moench] Voss), where preformed stem units contained within the apical bud constitute most of next season’s growth. Timing of bud set in white spruce shows genetic variation [3]. Our goal is to identify genes that exert genetic control over time to bud set in white spruce. As first steps towards that goal, we have conducted microarray gene expression profiling of shoot tips during the transition from active growth to dormancy in white spruce, and identified candidate regulators of bud formation by comparing these differentially expressed (DE) genes to results obtained from QTL analyses of time to bud set conducted using the same genes as molecular markers.

Regulation of shoot-system development in Populus

Shoot phenology interacts with crown morphology to determine leaf production and duration over the growing season and throughout a tree’s life span; and thus, this interaction has a major role in determining whole-tree photosynthesis and biomass yield. For several years, the pattern of shoot meristem activity determines Populus crown architecture, but after the first onset of flowering the specification of meristem identity (inflorescence vs. vegetative) also has a major influence on crown form. To study how shoot meristem activity and identity are regulated in Populus, we are focusing on two pathways that have been extensively characterized in annual plants: 1) the MORE AXILLARY BRANCHING (MAX) genes that are involved in the synthesis and perception of upwardly mobile strigolactones that inhibit axillary bud outgrowth, and 2) members of the TERMINAL FLOWER1 (TFL1)/FLOWERING LOCUS T (FT) and APETALA1(AP1)/FRUITFULL(FUL) gene families that regulate flowering. We are taking a multi-pronged approach that includes field and controlled-environment study of poplar transgenics, transcriptome analyses, cell-specific expression studies, and QTL and association mapping. QTL mapping in a hybrid poplar pedigree localized three of seven poplar MAX genes in QTL for bud set and two MAX genes in sylleptic branching QTL. All MAX transgenics were established in a field trial and phenotyping of phenology, crown morphology, and growth is in progress. Greenhouse studies of poplar transgenics with the seven different poplar MAX gene promoters driving the reporter gene GUS show that most of the MAX genes are expressed in vascular tissues. However, vascular expression patterns are different, especially in stems undergoing secondary growth. Surprisingly, none of the RNAi transgenics showed differences in branching in the greenhouse under standard growing conditions. High nitrogen levels can induce sylleptic branching in poplar and greenhouse experiments with MAX transgenics indicate a possible role for one MAX gene in nitrogen-induced sylleptic branching. Ongoing studies of the effects of decapitation of the shoot apex with and without subsequent auxin application to the cut stem indicate that, as predicted based on studies in annual plants, the poplar MAX RNAi transgenics show a reduced response to apically-applied auxin. Recent work has revealed that poplar FT1 and FT2 have diverged in regulation and function with FT1 promoting the transition to flowering in response to winter temperatures, whereas warm temperatures and long days promote FT2 expression and shoot growth [1]. In Arabidopsis, FT activates AP1, a key regulator of flower initiation. Expression and transgenic studies in poplar indicate that similar to the two poplar FTs, poplar AP1 subfamily members have roles in both flowering and bud set in response to short-days and abiotic stress. Ongoing work is aimed at defining the roles of FT and AP1 modules in these processes and to delineate the roles of the five different poplar AP1/FUL genes. Finally, TFL1 acts opposite to FT to promote vegetative meristem identity in Arabidopsis, and AP1 and TFL1 repress each other’s expression. The poplar TFL1 homologs, CEN1 and/or CEN2 have roles in maintaining vegetative identity and in the dormancy-growth transition [2] and we are currently working to define the individual roles of the poplar CENs and their relationships to FT and AP1 activities.

Association mapping of local adaptation traits of Scots pine in a European wide population sample

Traits related to local adaptation by definition show high phenotypic differentiation. The underlying genetic patterns could be clines at individual loci or small effects and extensive linkage disequilibrium at the underlying loci. In any case, including many populations in an analysis provides more information, but may simultaneously induce problems due to genetic structure. Even if the neutral loci have little genetic structure, loci related to other clinally selected traits could show more structure. Here we have developed an approach to efficiently use the information along a latitudinal environmental gradient. Scots pine populations from central Europe to the species' northern range were sampled and patterns of phenotypic variation of both timing of budset and frost tolerance were measured in common garden experiments, (10 populations, a total of 270 halfsib families, 25 trees per family). By hierarchical modelling of the phenotype's clinal variation and accounting for varying allele frequencies across the 10 populations, the statistical approach simultaneously exploits the genetic variation between and within populations to detect association signals. We apply shrinkage-based Bayesian variable selection to detect genetic associations between timing of bud set and ~450 SNPs in Scots pine.

Effect of dry and wet storage at cool temperatures on the post-harvest performance of Ranunculus asiaticus L. flowers

A study was undertaken to assess the effect of different storage temperatures on senescence and postharvest performance of isolated flowers of Ranunculus asiaticus L.. The main aim of the work was to develop a cost-effective storage protocol to reduce the postharvest losses and to bring out the transportation of cut flowers of R. Asiaticus. The flowers were subjected to two different storage treatments, dry storage and wet storage, and their postharvest performance was compared under laboratory conditions. For this purpose, the buds were harvested at 8:00 AM at loose bud stage (Stage II of flower development). The harvested buds were cut to a uniform size of 15 cm and processed for dry or wet storage. For dry storage, the buds were packed after wrapping them in moistened filter papers and kept at 5°C and 10°C. For wet storage, the buds were held in distilled water in separate glass beakers kept at 5°C and 10°C, respectively. A separate set of buds each for dry and wet storage was kept at room temperature (15±2)°C. After 72 h storage, the buds were kept at room temperature in distilled water. The average life of an individual flower that opened fully was about 4–5 days. The buds kept under wet storage at 5°C and 10°C for 72 h maintained their premature status, while the buds held at room temperature for 72 h generally bloomed. All the buds stored dry maintained their premature status irrespective of storage temperature. Storage of buds for 72 h at 5°C, followed by transferring to distilled water improved the longevity by about 5 to 6 days. Cold storage treatment before transferring to holding solution improved floral diameter, membrane integrity besides maintaining higher fresh and dry mass of flowers, sugar content, soluble proteins, and phenols. Our results suggested that wet and dry storage of premature buds of R. asiaticus for 72 h at 5°C, followed by placing them in distilled water, improved the cut flower longevity and can be used as effective postharvest storage treatments for this beautiful cut flower.

Functional and Expressional Analyses of PmDAM Genes Associated with Endodormancy in Japanese Apricot

Bud endodormancy in woody plants plays an important role in their perennial growth cycles. We previously identified a MADS box gene, DORMANCY-ASSOCIATED MADS box6 (PmDAM6), expressed in the endodormant lateral buds of Japanese apricot (Prunus mume), as a candidate for the dormancy-controlling gene. In this study, we demonstrate the growth inhibitory functions of PmDAM6 by overexpressing it in transgenic poplar (Populus tremula × Populus tremuloides). Transgenic poplar plants constitutively expressing PmDAM6 showed growth cessation and terminal bud set under environmental conditions in which control transformants continued shoot tip growth, suggesting the growth inhibitory functions of PmDAM6. In the Japanese apricot genome, we identified six tandemly arrayed PmDAM genes (PmDAM1-PmDAM6) that conserve an amphiphilic repression motif, known to act as a repression domain, at the carboxyl-terminal end, suggesting that they all may act as transcriptional repressors. Seasonal expression analysis and cold treatment in autumn indicated that all PmDAMs were repressed during prolonged cold exposure and maintained at low levels until endodormancy release. Furthermore, PmDAM4 to PmDAM6 responses to a short period of cold exposure appeared to vary between low- and high-chill genotypes. In the high-chill genotype, a short period of cold exposure slightly increased PmDAM4 to PmDAM6 expression, while in the low-chill genotype, the same treatment repressed PmDAM4 to PmDAM6 expression. Furthermore, PmDAM4 to PmDAM6 expression was negatively correlated with endodormancy release. We here discuss the genotype-dependent seasonal expression patterns of PmDAMs in relation to their involvement in endodormancy and variation in chilling requirements.

Repression of gibberellin biosynthesis or signaling produces striking alterations in poplar growth, morphology, and flowering

We modified gibberellin (GA) metabolism and signaling in transgenic poplars using dominant transgenes and studied their effects for 3years under field conditions. The transgenes that we employed either reduced the bioactive GAs, or attenuated their signaling. The majority of transgenic trees had significant and in many cases dramatic changes in height, crown architecture, foliage morphology, flowering onset, floral structure, and vegetative phenology. Most transgenes elicited various levels of height reduction consistent with the roles of GA in elongation growth. Several other growth traits were proportionally reduced, including branch length, internode distance, and leaf length. In contrast to elongation growth, stem diameter growth was much less affected, suggesting that semi-dwarf trees in dense stands might provide high levels of biomass production and carbon sequestration. The severity of phenotypic effects was strongly correlated with transgene expression among independent transgenic events, but often in a non-linear manner, the form of which varied widely among constructs. The majority of semi-dwarfed, transgenic plants showed delayed bud flush and early bud set, and expression of a native GAI transgene accelerated first time flowering in the field. All of the phenotypic changes observed in multiple years were stable over the 3years of field study. Our results suggest that transgenic modification of GA action may be useful for producing semi-dwarf trees with modified growth and morphology for horticulture and other uses.

FLOWERING LOCUS T duplication coordinates reproductive and vegetative growth in perennial poplar

Annual plants grow vegetatively at early developmental stages and then transition to the reproductive stage, followed by senescence in the same year. In contrast, after successive years of vegetative growth at early ages, woody perennial shoot meristems begin repeated transitions between vegetative and reproductive growth at sexual maturity. However, it is unknown how these repeated transitions occur without a developmental conflict between vegetative and reproductive growth. We report that functionally diverged paralogs FLOWERING LOCUS T1 (FT1) and FLOWERING LOCUS T2 (FT2), products of whole-genome duplication and homologs of Arabidopsis thaliana gene FLOWERING LOCUS T (FT), coordinate the repeated cycles of vegetative and reproductive growth in woody perennial poplar (Populus spp.). Our manipulative physiological and genetic experiments coupled with field studies, expression profiling, and network analysis reveal that reproductive onset is determined by FT1 in response to winter temperatures, whereas vegetative growth and inhibition of bud set are promoted by FT2 in response to warm temperatures and long days in the growing season. The basis for functional differentiation between FT1 and FT2 appears to be expression pattern shifts, changes in proteins, and divergence in gene regulatory networks. Thus, temporal separation of reproductive onset and vegetative growth into different seasons via FT1 and FT2 provides seasonality and demonstrates the evolution of a complex perennial adaptive trait after genome duplication.

Challenges in studies on flowering time: interfaces between phenological research and the molecular network of flowering genes

AbstractFlowering time is a well‐studied subject in ecology, evolution and molecular biology. Long‐term phenological studies have shown relationships between flowering time and environmental and endogenous factors in many species. In contrast, molecular studies using model plants have revealed a complex regulatory network of flowering. We propose that flowering would be a model trait for the integrated study of ecology, evolution and molecular biology. We introduce briefly the flowering regulatory pathways of Arabidopsis thaliana, followed by molecular techniques such as transgenic manipulation, quantitative real‐time PCR and detection of differentially expressed genes that could facilitate the study of ‘nonmodel’ species of ecological interest but with little available genome information. Application of the flowering gene network to wild species will be illustrated by two examples: modeling and prediction of the expression of flowering genes in Arabidopsis halleri, and the latitudinal cline of bud set and cessation in Populus. Finally, we discuss the challenges in integrating knowledge of the regulatory network on flowering into ecologically unique flowering phenomena such as synchronous intermittent mass flowering—the topic of this special issue.

Temperature signals contribute to the timing of photoperiodic growth cessation and bud set in poplar

Bud set, the cornerstone delimiting the seasonal growth period in trees, is the dynamic net result of the often photoperiod-controlled growth cessation and the subsequent bud formation. Here, we show that in hybrid poplar, the critical day length for growth cessation and the duration of bud formation each vary with local climatic conditions in identical genotypes. The detailed dissection of bud set suggests temperature as one additional environmental factor that modifies the sensitivity to day-length signals at growth cessation and influences the duration of bud formation in poplar. The ability of perennial plants to integrate additional environmental signals with photoperiod signaling may add to short-term acclimatization to the predicted longer growing seasons in future climates.

QTL mapping in white spruce: gene maps and genomic regions underlying adaptive traits across pedigrees, years and environments.

BackgroundThe genomic architecture of bud phenology and height growth remains poorly known in most forest trees. In non model species, QTL studies have shown limited application because most often QTL data could not be validated from one experiment to another. The aim of our study was to overcome this limitation by basing QTL detection on the construction of genetic maps highly-enriched in gene markers, and by assessing QTLs across pedigrees, years, and environments.ResultsFour saturated individual linkage maps representing two unrelated mapping populations of 260 and 500 clonally replicated progeny were assembled from 471 to 570 markers, including from 283 to 451 gene SNPs obtained using a multiplexed genotyping assay. Thence, a composite linkage map was assembled with 836 gene markers.For individual linkage maps, a total of 33 distinct quantitative trait loci (QTLs) were observed for bud flush, 52 for bud set, and 52 for height growth. For the composite map, the corresponding numbers of QTL clusters were 11, 13, and 10. About 20% of QTLs were replicated between the two mapping populations and nearly 50% revealed spatial and/or temporal stability. Three to four occurrences of overlapping QTLs between characters were noted, indicating regions with potential pleiotropic effects. Moreover, some of the genes involved in the QTLs were also underlined by recent genome scans or expression profile studies.Overall, the proportion of phenotypic variance explained by each QTL ranged from 3.0 to 16.4% for bud flush, from 2.7 to 22.2% for bud set, and from 2.5 to 10.5% for height growth. Up to 70% of the total character variance could be accounted for by QTLs for bud flush or bud set, and up to 59% for height growth.ConclusionsThis study provides a basic understanding of the genomic architecture related to bud flush, bud set, and height growth in a conifer species, and a useful indicator to compare with Angiosperms. It will serve as a basic reference to functional and association genetic studies of adaptation and growth in Picea taxa. The putative QTNs identified will be tested for associations in natural populations, with potential applications in molecular breeding and gene conservation programs. QTLs mapping consistently across years and environments could also be the most important targets for breeding, because they represent genomic regions that may be least affected by G × E interactions.

Nutrient Accumulation and Flower Bud Formation Affected by the Time of Terminal Bud Set on Water Sprouts of Persimmon

Heavy pruning to lower tree height of persimmon results in excessive production of water sprouts and reduced yield. This experiment was conducted on ‘Fuyu’ (Diospyros kaki) trees to assess if the time for terminal bud set of water sprouts affected flower bud formation. Some sprouts were not pruned to serve as fruiting branches for the next season. Thirty to 40 water sprouts were tagged in 2005 and 2006, the growth of which stopped from mid-June to late August. The later terminal buds set, the lower the percent dry weight in the apical 10 cm. The apical segments of sprouts that continued to grow to mid- to late August were characterized by low soluble sugars, starch, and inorganic elements such as nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) compared with those that set terminal buds earlier. The number of flower buds from the water sprouts that set terminal buds by early August the previous year bore more than 12 flower buds the next year, whereas those that grew to mid- to late August bore fewer than three. It was concluded that water sprouts could be used as fruiting branches for the next year as long as terminal buds set by early August, thereby alleviating yield reductions that come with heavy pruning.

Effects of different pH sprays on the efficiency of prohexadione-Ca in sweet cherry trees

Abstract In 2003 and 2004, young ‘Kordia’ sweet cherry trees were sprayed with prohexadione-Ca (Pro-Ca) to control tree growth and stimulate flower bud setting. A rate of 200 mg Pro-Ca l-1 × 2 dissolved in various pH-buffered (6.0-4.5) aqueous solutions was used. Regardless of the acidity of the spray solution applied, the trees treated with Pro-Ca were characterised by reduced shoot and internode length, greater number of shoots (2003) and increased total shoot extension (2004) relative to the control. In both years, Pro-Ca applied in a pH-4.5 buffer solution contributed to an increase of flower bud clusters on current-season shoots. However, there were no significant differences among Pro-Ca/pH treatments either in the vegetative or generative characteristics studied. Two years after Pro-Ca application, no residual effects were found in the studied tree characteristics.

Gene expression changes during short day induced terminal bud formation in Norway spruce

The molecular basis for terminal bud formation in autumn is not well understood in conifers. By combining suppression subtractive hybridization and monitoring of gene expression by qRT-PCR analysis, we aimed to identify genes involved in photoperiodic control of growth cessation and bud set in Norway spruce. Close to 1400 ESTs were generated and their functional distribution differed between short day (SD-12 h photoperiod) and long day (LD-24 h photoperiod) libraries. Many genes with putative roles in protection against stress appeared differentially regulated under SD and LD, and also differed in transcript levels between 6 and 20 SDs. Of these, PaTFL1(TERMINAL FLOWER LIKE 1) showed strongly increased transcript levels at 6 SDs. PaCCCH(CCCH-TYPE ZINC FINGER) and PaCBF2&3(C-REPEAT BINDING FACTOR 2&3) showed a later response at 20 SDs, with increased and decreased transcript levels, respectively. For rhythmically expressed genes such as CBFs, such differences might represent a phase shift in peak expression, but might also suggest a putative role in response to SD. Multivariate analyses revealed strong differences in gene expression between LD, 6 SD and 20 SD. The robustness of the gene expression patterns was verified in 6 families differing in bud-set timing under natural light with gradually decreasing photoperiod.